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Full text of "The geology of the Shepaug aqueduct tunnel, Litchfield County, Connecticut"

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state of Connecticut 

PUBLIC DOCUMENT No. 47 



State Geological and Natural 
History Survey 

W. E. BRIXTON, Superintendent 



BULLETIN NO. 40 




HARTFORD 

Printed by the State Geological and Natural History Survey 

1927 



State Geological and Natural History Survey 
of Connecticut 



COMMISSIONERS 

John H. Trumbull, Governor of Connecticut 
James Rowland Angell, President of Yale University 
James Lukens McConaughy, President of IVesleyan University 
Remsen Brinckerhoff Ogilby, President of Trinity College 
Charles Lewis Beach, President of Connecticut Agricultural College 
Benjamin Tinkham Marshall, President of Connecticut College for 
Women 

SUPERINTENDENT 

W. E. Brixton 

Agricultural Experiment Station, New Haven 



DISTRIBUTION AND EXCHANGE AGENT 

George S. Godard, State Librarian 

Hartford 



The Geology of the Shepaug Aqueduct 

Tunnel 

Litchfield County, Connecticut 

By 

WILLIAM MACDONOUGH AGAR, Ph.D. 
Assistant Professor of Geology, Yale University 

with a chapter by 

ROBERT A. CAIRNS, C.E. 
City Engineer, Water bury, Conn. 




HARTFORD 

Printed by the State Geological and Natural History Survey 

1027 



1/ 



qE^^. SSA2. 



CONTENTS 



Page 

Preface g 

Introduction ii 

Topography and Drainage ii 

History of the Project — by Robert A. Cairns, City Engineer, 

Waterbury 13 

General Geology . .16 

The Hartland Schist 19 

Structure 22 

Faults 24 

Metamorphism of the Hartland Schist 24 

The Berkshire Schist 26 

The Brookfield Diorite , . 28 

The Schist Inclusions in the Diorite 31 

The Mount Tom Hornblende Gneiss 32 

The Thomaston Granite Gneiss 33 

Buried Surface Features Exposed by the Tunnel and the Diamond 

Drill Holes . 35 

Pre-Pleistocene Weathering Preserved South of Mount Prospect . 35 

The Pre-Glacial Surface under the North End of Bantam Lake . 35 

Summary 36 

Bibliography 37 



1 4fi^44 



ILLUSTRATIONS 

MAPS 

Geological Map of Tunnel Area, facing page i6. 
Profile Map of Tunnel, facing page 20. 

FIGURES 

1. Index map of Connecticut. Shaded portion shows area included in this 

report. 

2. Map showing watersheds in area discussed. — . — . — , Watersheds ; AA, 

Tunnel line; — , Line of diamond drill holes. (See Fig. 3.) 

3. Cross Section of Bantam Lake and Cranberry Swamp. 

PLATES 

I. a. View looking up the Shepaug River Valley, soon to be turned 
into a reservoir. Tunnel entrance to the right of the shacks. 
Photograph by B. H. Walden. 
b. View looking into entrance of tunnel from across the Shepaug 
River, along the line of the proposed dam. 

II. a. View Looking down the Shepaug River from below the site of 
the proposed dam. Part of the dump from the tunnel excava- 
tion is shown at the left. 
b. View showing the massive character of the Brookfield diorite at 
the entrance to the tunnel east of the Bantam River crossing. 

III. a. View looking across the narrows of Bantam Lake from Dempsey's 

Point to Marsh's Point. The tunnel passes under the lake 
between these points, 
b. Valley of the West Branch of the Naugatuck River above the 
present Morris Reservoir and just below the tunnel outfall, 
where the waters of the Shepaug River will be brought through 
the tunnel and impounded. 

IV. Irregular contact between the Berkshire schist and a pegmatite dike 

in the tunnel, 1000 feet east of the tunnel entrance at the 
Shepaug River. Two drill holes are shown in the schist at 
the left. Photograph by B. H. Walden. 

V. a. Quartz monzonite porphyry dike cutting the massive diorite in 

the tunnel under Bantam Lake. Photograph by B. H. Walden. 

b. Pegmatite lenses parallel with the flat dipping foliation of the 

Hartland mica schist, 1000 feet east of the southernmost corner 

in the tunnel. Photograph by B. H. Walden. 

VI. a. Hartland mica schist showing crystalloblastic texture. Crossed 
nicols X 25. 
b. Berkshire schist from west end of tunnel showing curved biotite 
flakes (B) and quartz (Q) partly granulated. An incipient 
cataclastic texture superimposed upon a crystalloblastic texture. 
Crossed nicols x 25. Photograph by D. Selchow. 

VII. a. Brookfield diorite near center of tunnel showing texture of 
crystallization. (H.) hornblende; (B) biotite; (P) plagioclase 
(mostly andesine). Plane polarized light x 40. 



O CONNECTICUT GEOL. AND NAT. HIST. SURVEY 

b. Biotite hornblendite near center of tunnel showing texture of 
crystallization. (H) hornblende; (B) biotite; (T) colorless 
amphibole grading into the hornblende. Plane polarized light 
X 40. 

VIII. a. Hartland schist included in Brookfield diorite showing large 
crystal of andesine, strained throughout and somewhat crushed 
along the edges and in a line through center ; granulated quartz, 
and biotite bent around the more resistant fragment. Shows 
mortar texture. Crossed nicols x 25. 
b. Mount Tom hornblende gneiss showing pulverized plagioclase (P), 
larger individuals of quartz (Q) and hornblende (H) project- 
ing as fine needles into pulverized plagioclase. Protoclastic 
texture with beginning of recrystallization. Crossed nicols 
x 40. Photograph by D. Selchow. 



PREFACE 

This bulletin presents the results of a detailed study of the 
geology of the Shepaug Aqueduct Tunnel and the area immedi- 
ately surrounding it in the town of Litchfield, near the center of 
the western upland of Connecticut. 

The tunnel was drilled by the city of Waterbury as a part of 
an extension of its reservoir system, and this bulletin contains 
a chapter by R. A. Cairns, C.E., city engineer of Waterbury, 
giving the history of the project and the city's reasons for going 
to this particular region for additional water. 

The geological investigation was undertaken in the tunnel in 
order to study the seven-mile section so exposed before any part 
of it was hidden by lining. It was an unusual opportunity to 
examine a continuous section of the complicated metamorphic 
rocks of the western upland of Connecticut, and much has been 
learned concerning the details of structure and petrography of the 
Berkshire and Hartland schists, the two most widespread forma- 
tions, as well as of many less widely distributed. Such details are 
presented here as a record of the geology of the region itself and 
because of their bearing upon the problems of the geology of 
western Connecticut and the neighboring areas. 

The field work occupied part of the summers of 1925 and 1926, 
and the petrographic work was done in the laboratory of Yale 
University during the winter of 1926- 1927. 

The writer wishes to thank Mr. R. A. Cairns and the whole 
engineering staff in the field, particularly Mr. I. F. Story, engi- 
neer in charge, for unfailing interest in the work and for assist- 
ance rendered in many ways. He also wishes to acknowledge 
the helpful criticism of Mrs. A, Knopf and the help of Professor 
A. Knopf in the identification of certain minerals in thin section. 



GEOLOGY OF THE SHEPAUG AQUEDUCT TUNNEL,, 
LITCHFIELD COUNTY, CONNECTICUT 

William M. x\gar 
Introduction 

The Shepaug tunnel bears in a general northwest-southeast 
direction across that part of Litchfield County immediately south 
of Litchfield village. It is designed to carry the waters of the 
West Branch of the Shepaug River under the intervening hills 
and the bed of Bantam Lake to the West Branch of the Naugatuck 
River above the northern extremity of the Morris Reservoir, part 
of the present Waterbury water system. 

The tunnel level is such that it comes to the surface at the 
crossing of the Bantam River, two-fifths of a mile southwest of 
Bantam village, and lies above bed rock in a low swampy area 
one-quarter of a mile west of there. This made it possible to drill 
the tunnel in three separate sections without sinking any shaft. 
The westernmost section is a straight tunnel bearing south 81'' 27' 
east. This part was drilled east from the valley of the Shepaug 
at a point about one and a quarter miles north of Woodville — the 
intake point — and west from the westernmost end of the swamp 
referred to above. An open cut v/as made through the swamp 
and this was later cemented and filled. A short section was 
drilled west from the Bantam River crossing on the same bearing, 
to meet the eastern edge of the swamp. The grade of this part 
of the tunnel is 0.08%. 

The eastern section begins just across the Bantam River valley 
and follows the same bearing for 6180 feet with a 0.5% grade to 
the broad base of Dempsey's Point on the north shore of Bantam 
Lake. From there it bears S. 35° 46' E. for 4540 feet, passing 
under the lake and skirting the shore of Marsh's Point to the 
bottom of the bay, and then turns again to S. 81° 30' E. and holds 
that direction as far as the outfall above the Morris Reservoir. 
The grade is 0.1% from the first corner to the outfall. This 
section of the tunnel was drilled from the Bantam River and out- 
fall ends and the tunnels met 2.15 miles from the outfall. 

The total length of the tunnel is 38235.67 feet or 7.24 miles and 
all but the 570 feet under the marsh and the 697 feet at the 
Bantam River crossing are drilled through solid rock. The 
difference in elevation between the intake and outfall amounts to 
62 feet. 

Topography and Drainage 

The region underlain by the tunnel lies near the center of the 
western upland of Connecticut. It is maturely dissected with hills 



12 CONNECTICUT GEOL. AND NAT. HIST. SURVEY [Bull. 

rising to more or less accordant levels, lower on the southeast and 
higher on the north and west. Much of the surface has been built 
up above its pre-Pleistocene level by glacial deposits and lake or 
swamp deposits and shows youthful features superimposed upon 
the mature topography. Besides this the ancient erosion surface 
that was elevated and dissected was far from smooth, and many 
irregularities remained to form the high points in the present 
erosion cycle. 

Mount Prospect, 1365 feet, northwest of the center of the area, 
and Rabbit Hill, 1340 feet, along the western edge, are the highest 



Fig. I. — Index map .of Connecticut. Shaded portion shows area included 

in this report. 



elevations, while Mount Tom, Little Mount Tom, and Mount Rat, 
a group of steep hills in the southwest corner, compose the most 
rugged part of the region. The lowest point is also in the south- 
west corner where the Shepaug River leaves the map area at an 
elevation of 560 feet after receiving the Bantam River as a 
tributary. 

Bantam Lake lies in a depression in the south central part of 
the region. It is bounded on the northeast by a swamp and a 
sand plain several square miles in extent, and on the southwest by 
another swamp bordered by rolling, sandy hills. A number of 
interesting discoveries relating to the pre-Pleistocene surface under 



No. 40] 



GEOLOGY OF SHEPAUG TUNNEL 



13 



the north end of Bantam Lake were made during the construction 
of the tunnel and will be mentioned at the end of this report. 

The region is drained by three streams (Fig. 2). The Bantam 
River has the largest watershed. It includes Bantam Lake and 
cuts through the center of the map and joins the Shepaug River 
near the southwest corner. The westernmost watershed and the 
next largest is drained by the Shepaug River, while the smallest 
one of the three is occupied by the West Branch of the Naugatuck 
along the eastern margin of the area. The Bantam River enters 
the Shepaug and together they are tributary to the Housatonic 



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Fig. 2. — Map showing watersheds in area discussed. — . — . — . — . — , 

Watersheds. AA, Tunnel line. , Line of diamond drill 

holes (see Fig. 3). 



further west. The West Branch of the Naugatuck drains into the 
main Naugatuck which itself is tributary to the Housatonic some 
miles south of where the Shepaug enters that stream. 

There are a number of small tributaries, ponds, and marshes 
included within these drainage systems, but Mount Tom Pond, the 
largest body of water next to Bantam Lake, though it lies within 
the area drained by the Bantam River, has no visible inlet or 
outlet and, on the surface, at any rate, belongs to none of them. 

History of the Project 
By R. A. Cairns, City Engineer, Waterhury 

The Shepaug Tunnel became a necessary adjunct of the water 
supply system of the City of Waterbury as a natural step in a 
development resulting from a long series of happenings beginning 



14 CONNECTICUT GEOL. AND NAT. HIST. SURVEY [Bull. 

with the initial construction of reservoirs and distribution mains 
in 1869. Much criticised and objected to at that time as of doubt- 
ful wisdom, the project of a public water supply was successful 
from the start and from decade to decade the demand for water 
unfailingly and soon exceeded the capacity of reservoirs frequently 
enlarged. 

In 1893 the futility of frequent and small additions was recog- 
nized and the city took the radical step of penetrating into the 
Litchfield hills, securing diversion rights to 18 square miles of 
watershed on the West Branch of the Naugatuck River in the 
towns of Watertown, Thomaston, Morris and Litchfield, creating 
a reservoir many times larger than any it had built before, and 
laying a 36-inch pipe line ten miles long. But although this was 
believed to be almost a final solution of the potable water supply 
for Waterbury and its suburbs, the continued growth of the com- 
munity at a rate totally unexpected by the conservative citizen, 
compelled a serious study as early as 1907 of the possibilities of 
further resources on a still larger scale. 

There were several areas from which an additional supply of 
substantial size could be obtained. Of these, the natural and most 
readily accessible was that above the village of Litchfield along 
Bantam River. Opposition was offered to this scheme on the 
ground that it would be destructive to the attractions of Bantam 
Lake, which has a large summer colony bringing trade to the 
adjoining towns and benefiting them by the creation of a large 
amount of taxable property. This opposition succeeded in obtain- 
ing from the State Legislature an act prohibiting the City of 
Waterbury from diverting any water from Bantam Lake or from 
any of the tributaries. A similar act was afterward passed in 
relation to Waterbury taking water from the Naugatuck River 
above Torrington. 

There then remained as the most feasible project the diversion 
of water from the Shepaug River, where that stream forms the 
dividing line between the towns of Litchfield and Warren. Here 
it was seen that a reservoir of large size could be formed having 
tributary to it about 37 square miles of sparsely settled hilly coun- 
try, largely wooded and with a very small percentage of swamps. 
Analysis of the water showed it to be of satisfactory quality, 
unusually soft, coming from a region devoid of limestone or other 
formations tending to produce a hard water. A further attraction 
is that the area is subject to very little attrition during periods of 
heavy rain. 

The chief legal difficulty in connection with this undertaking 
lay in obtaining rights to divert the water from one watershed 
into another and in obtaining satisfactory adjustments with the 
many interests along the Shepaug and Housatonic Rivers. These 
matters, however, were finally settled in a manner apparently 
satisfactory to all parties concerned, provision being made to 



No. 40] GEOLOGY OF SHEPAUG TUNNEL 1 5 

maintain a certain minimum flow in the stream, some properties 
being purchased outright, conditional agreements for deferred 
takings being made with others and in one instance a substantial 
payment in money representing present value of estimated future 
damages. 

The main physical problem in this Shepaug development lay in 
finding the best method of conveying water to the City. In this 
part of the State, as indeed in most others, the water courses run 
north and south, separated by ridges of hills. It was found that 
a gravity pipe line could be built which would carry water all the 
way to the City without tunnels or excessively deep cuttings, but 
it must follow such a devious course that its length would exceed 
21 miles, and much of it would lie in regions not easily reached 
by vehicles. Other and shorter routes to the City were studied, 
involving varying lengths of tunnel. It was found that a line 
almost due east would take water to existing reservoirs in the 
West Branch Valley, but that its length of about jYa miles would 
of necessity be substantially all so far below the surface of the 
ground as to require tunneling. No satisfactory site for a regu- 
lating reservoir near the City appearing, and direct connection 
with existing reservoirs by tunnel presenting certain advantages 
over the long pipe line of necessarily limited capacity, it was 
finally determined to undertake the driving of the long tunnel. 

After careful surveying of the line, a large number of diamond 
drill borings were made to determine the elevation of rock and 
to get some information as to its character and its water-bearing 
qualities. Particular attention was given to the Bantam Lake 
Basin, containing the largest natural body of fresh water in the 
State. Here a serious difiiculty was encountered. It was found 
that the northern part of the lake consisted of a deep bowl in the 
rock filled in to a thickness of a hundred feet or more with sand 
and silt. Here the surface of the rock lies below the grade line 
of a self-draining tunnel, necessitating an inverted syphon to keep 
in the rock. Such a drop in the tunnel would form a pocket a 
mile long, expensive to construct, always full of water after opera- 
tion of the aqueduct began, and requiring special pumping arrange- 
ments to make it accessible for inspection. 

Desiring to avoid this condition, and tunnel driving under air 
pressure at such a depth being quite impracticable, thus barring 
any location except in rock where work proceeds under atmos- 
pheric pressure, a reconnaissance with the diamond drill was 
undertaken and it was found that on a line crossing the lake at 
the narrows and continuing under Marsh's Point to Sandy Beach 
the rock was high enough at all points to afford at least a minimum 
amount of cover for the tunnel. The original location was 
accordingly changed and the tunnel driven on this line, having two 
angles in it, instead of being straight as originally proposed. 

Driving of the tunnel was begun in December, 192 1. The 



1 6 CONNECTICUT GEOL. AND NAT. HIST. SURVEY [Bull. 

westerly section between Shepaug and Bantam Rivers was holed 
through in April, 1926, and the easterly section was holed through 
in September of the same year. For much of the way the rock 
strata was found so solid or so interlocked as to make it unneces- 
sary to support the roof, either temporarily or permanently. A 
singularly small amount of water was encountered, even where for 
more than a mile the tunnel penetrated under Bantam Lake and its 
basin. No especially troublesome faults were found. 

General Geology 

The region is underlain by igneous and metamorphic rocks that 
comprise two schist series ; a diorite intrusion, in part gneissic ; a 
hornblende gneiss ; and still younger granite and pegmatite intru- 
sions. 

The two schists, the Berkshire and the Hartland, are the oldest 
rocks of the region. They are quite distinct in the field and are 
not believed to be of like age. They lie next to each other in 
many places but occur in discontinuous, scattered outcrops with- 
out any visible contact and, unluckily, the tunnel cuts through 
an area where the two are separated by several miles of diorite, 
intrusive into both. 

The legend attached to the accompanying map does not assign 
any definite geological age to the formations exposed in this 
area. It is thought best to place the rocks in their relative posi- 
tions according to the structural and petrographic evidence in the 
region and to await dating the series until work in the surrounding 
regions affords more convincing evidence than any on hand at 
present. The map is taken from the Litchfield Quadrangle, 
Conn.-N.Y., pubHshed by the United States Geological Survey. 

In 1894 R. Pumpelly^ made the Hoosac schist, on the east flank 
of Hoosac Mountain, equivalent to the whole of the Stockbridge 
limestone, Berkshire schist. Bellows-pipe limestone, and part at 
least of the Greylock schist lying west of that same mountain. 
Pumpelly^ believed he had evidence that the Stockbridge limestone 
graded laterally into the Hoosac schist along the western base of 
Hoosac Mountain and in the valley of the Hoosic River. The 
Cambrian Vermont formation and the pre-Cambrian Stamford 
gneiss underlie the Hoosac schist and compose the core of the 
Mountain. 

The Hoosac Mountain ridge marks the beginning of the Green 
Mountain anticlinorium in Massachusetts, an elevated plateau that 
extends north and south through the western part of the State and 
separates the lowland of the Connecticut River on the east from 
the Housatonic Valley on the west. The plateau is composed of 



^ Geology of the Green Mountains in Massachusetts, by Raphael Pumpelly, T. Nelson 
Dale, and J. E. Wolff, U. S. G. S. Monograph 23, 1894. 
' Op. cit. pp. I4-I7. 



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Geological Map of the Tunnel Area 
Bull, 40, Conn. Geol. & Nat. Hist. Survey 



Miles 

Contour l-nterval = 4-Oft. 



No. 40] GEOLOGY OF SHEPAUG TUNNEL 1 7 

pre-Cambrian rocks flanked on the east by the Hoosac schist over- 
lain by the Rowe schist, and on the west by the Dalton formation, 
the Cheshire quartzite, the Stockbridge limestone, and the Berk- 
shire schist. The Stockbridge limestone is the valley formation of 
the Housatonic lov^land. The Cheshire and Dalton lie as isolated 
patches along the border of the upland or project into it as spurs 
and, together with the Berkshire schist, form the isolated hills that 
rise above the valley floor. This area has been the subject of a 
number of papers by B. K. Emerson, culminating in "The Geology 
of Massachusetts and Rhode Island," published in 191 7 as Bulletin 
597 of the United States Geological Survey. In the correlation 
tables facing page 17 the Hoosac schist and Rowe schist are made 
the equivalent of the Berkshire — all of Ordovician age. That is, 
the Hoosac is taken entirely out of the Cambrian and much 
restricted in the Ordovician. 

The Green Mountain anticlinorium enters northwestern Con- 
necticut as the Norfolk Hills and passes out of the State into 
southeastern New York as a belt of highlands including Barrack 
Mountain, Cream Hill, and Sharon Mountain. It is intersected 
by the Housatonic River which leaves the westerly swinging lime- 
stone valley to cross the highlands in a narrow north-south gorge. 

The Hoosac schist passes down into Connecticut as a continuous 
strip of varying width lying along the eastern edge of this anti- 
clinorium and is known as the Hartland schist.^ The Dalton 
formation, the Cheshire quartzite, Stockbridge limestone and Berk- 
shire schist maintain their position on the west of the axis until 
the latter swings southwest out of the State. At this point the 
supposedly younger series bridges the pre-Cambrian plateau and 
the Berkshire schist is widely developed in the hills of Cornwall 
and Kent and comes into contact with the Hartland schist in the 
neighborhood of Litchfield. The Cheshire quartzite and the 
Stockbridge limestone are also at present^ represented as occurring 
south of the plateau in long narrow bands though there is con- 
siderable doubt concerning the equivalence of these to the forma- 
tions north of the plateau. 

A word must be included here concerning the Berkshire forma- 
tion as it is now mapped in Connecticut. (See reference above.) 
It forms at least two very distinct types, namely, that on the Mount 
Washington range, the extension of the Taconic Mountains into 
Connecticut, a greenish sericite, chlorite schist with considerable 
albite and local development of garnet ; and the Canaan Mountain 
type, a quartz, biotite schist or a gneiss with as much as ten per 
cent of oligoclase and considerable amounts of garnet, staurolite 

1 The Hartland schist may represent in part the Rowe schist of Massachusetts that 
overlies the Hoosac. It is tentatively considered here as being equivalent to the Hoosac 
as stated by Rice & Gregory, Manual of the Geology of Conn., Conn. Geol. & Nat. Hist. 
Survey, Bull. 6, 1906. 

2 H. E. Gregory and H. H. Robinson, Preliminary Geological Map of Connecticut, 
Bulletin No. 7, Connecticut Geological and Natural History Survey, 1907. 



1 8 CONNECTICUT GEOL. AND NAT. HIST. SURVEY [Bull. 

and sillinianite irregularly distributed. The hills that rise above 
the Housatonic valley floor between these two nearly connect the 
types petrographically as well as areally, and there seems to be 
little question that they belong to the same formation. 

The Canaan Mountain type of Berkshire is the one that laps 
over the Green Mountain anticlinorium and that comes into contact 
with the Hartland schist both north and south of Bantam Lake. 
The latter two rocks are quite dissimilar and are believed to have 
suffered a different amount of metamorphism. In fact, if the cor- 
relation be based upon this region alone and the western series, 
discontinuous with the Berkshire to the North, can be proved with- 
out question to be the Berkshire, then the Berkshire must be called 
the older rock. 

The Brookfield diorite, a medium to coarse-grained greenish 
diorite and quartz diorite with gneissoid and even schistose phases, 
cut by later dikes of diorite porphyry, granite, pegmatite and dark 
green biotite hornblendite, and including stringers of the Hart- 
land schist, forms the central part of the area. It stretches from 
the outskirts of Litchfield village on the northeast to Mount Tom 
on the southwest and underlies most of Bantam Lake. At its 
northwestern extremity on Mount Prospect it is intersected by a 
comolex set of intrusives, gabbros and related rocks correlated by 
W. H. Hobbs^ with the Cortland Series near Peekskill, New York. 
That area is being studied in detail by E. McKnight and is not 
described in any detail in this bulletin. 

At the southwest extremity of the diorite there lies an irregular 
area of green and white hornblende gneiss. It forms Mount Tom, 
Little Mount Tom, and Mount Rat, and projects about one mile 
to the southwest of the latter hill. This rock, known as the Mount 
Tom hornblende gneiss, forms dikes in the Hartland schist along 
the northwest slope of Mount Rat and has a much more perfectly 
developed foliation in the dikes and along its edges than near the 
center of the mass. It represents an intrusion that suffered 
deformation before its solidification was completed. 

It will be seen that this surface distribution of rocks eliminates 
the area of Rough quag quartzite featured on the geological map of 
Connecticut of 1907^ as underlying Bantam Lake and covering 
considerable areas both to the east and west, south of the lake. 
The reason for this change will be discussed in detail further 
along. Briefly, it is that the ledges that outcrop over this area are 
quartz schist identical with many of the layers forming an impor- 
tant part of the Hartland schist series as exposed in the tunnel. 

The northwest section of this region is underlain by the 
Thomaston granite gneiss. It occurs throughout the neighboring 



1 On Two New Occurrences of the "Cortland Series" of Rocks within the State of 
Connecticut. W. H. Hobbs, Festschrift zum Siebzigste Geburstage H. Rosenbusch, 
^S-48 Stuttgart 1906. 

2 Gregory and Robinson, Bull. No. 7. 



No. 40] GEOLOGY OF SHEPAUG TUNNEL 1 9 

region as dikes and stocks of granite or its gneissic equivalent 
and cuts all of the other rocks, excepting the pegmatite dikes. 

The relations of the strata south of the granite and west of the 
diorite are very complicated. The geological map of Connect- 
icut shows several disconnected areas of Becket gneiss (referred 
to the pre-Cambrian) and Berkshire schist. According to that 
interpretation the first several thousand feet of the tunnel pass 
through the Becket gneiss. Reasons will be given in this 
bulletin for including all of this complex within the Berkshire 
formation and omitting the Becket altogether. 

The remaining rocks of the region mapped include the pegma- 
tite dikes and the relatively much rarer quartz veins. These do 
not appear very frequently on the surface though there is a large 
pegmatite dike forming a bare knob in a field one mile northeast 
of Woodville, but they are very common in the tunnel, and imme- 
diately east of this area the Hartland schist is disrupted by a great 
quantity of pegmatites ranging from large-sized dikes to minute 
injections. Underground the pegmatites are found in large num- 
bers in both the Berkshire and the Hartland schists and in much 
smaller numbers in the Brookfield diorite. The quartz veins have 
about the same relative distribution but are much less common. 

The foliation of the metamorphic rocks throughout the area 
strikes N. 50° E. to N. 10° W., generally about N. 20° E. ; and 
the dips, which are nearly always towards the west, vary from 
vertical to about 30°. The only exception to this uniform strike 
and dip is in the easterly part of the diorite area where the folia- 
tion of the gneissoid diorite and the included fragment of schist 
strikes northwest and dips east. 

The tunnel exposes the contact between the Brookfield diorite 
and the Berkshire schist on the west and between the Hartland 
schist and the diorite on the east. The westernmost contact is 
not very definite. The igneous rock has penetrated the schist as 
sills parallel to the foliation and two areas of the schist occur some 
distance within the igneous rock. The eastern contact is sharp 
although there are many fragments of the Hartland series included 
in the diorite far from the contact. 

The fragments of included schist from both formations are 
somewhat different from their corresponding types but there is no 
marked amount of contact metamorphism to be noted in either 
case. 

The Hartland Schist 

The Hartland schist is a widespread formation that extends in 
relatively narrow belts from northern Massachusetts, where it is 
known as the Hoosac schist, through the western part of Con- 
necticut to Long Island Sound. The small area considered in this 
report cannot be regarded as including all the varieties present in 
the formation but the tunnel exposes a section two and three- 



2 CONNECTICUT GEOL. AND NAT. HIST. SURVEY [Bull. 

quarters miles long nearly at right angles to the strike of the 
foliation and gives the longest continuous section of the schist in 
the State of Connecticut. 

The Hartland formation as exposed in this state was described 
in some detail by Rice and Gregory.^ They state on page 97: 
"The rock is everywhere a mica schist of definable character, but 
exhibits great variation in texture, composition, and field appear- 
ance. Its aspect has been rendered still more complicated by the 
intrusion of igneous rock on a large and a small scale. Where 
least affected by intrusion, the rock appears as a highly fissile 
schist ... In color it ranges from clear metallic muscovite in 
West Granby, to a black biotite mixed with graphite further 
south." Garnet is said to be almost always present and cyanite to 
be scattered sparingly throughout almost the whole extent of the 
schist, while staurolite is only locally developed. 

The general description summarized above fits the Hartland of 
this section in a broad way but there is one very important dif- 
ference. There are two distinct facies of schist exposed in the 
tunnel and in the neighboring outcrops, namely a fissile, lustrous 
schist corresponding to the above description, and a quartz schist 
of totally different aspect. The latter type is a greenish white 
to brown or bronze rock which cleaves along planes due to the 
development of mica in bands but shows a great deal of quartz 
when broken across the cleavage. The two types represent orig- 
inal differences in composition, since they alternate as do sedi- 
mentary strata, and first one and then the other will form the 
dominant rock. 

The base of the Hartland (Hoosac) schist exposed along 
the eastern edge of the Green Mountain anticlinorium in Mas- 
sachusetts is a coarse garnetiferous mica gneiss. It rests 
unconformably upon the underlying rocks and is overlain by a 
non-garnetiferous series of alternating sandy and micaceous 
layers.^ Such a succession parallels the distribution of the series 
in Connecticut where with a westerly dip, the eastern beds are 
characteristically full of garnets while the upper layers, repre- 
sented by the tunnel section, are prevailingly non-garnetiferous 
quartz and mica schists. 

The structure of the series as a unit, the amount of repetition 
by folding or by thrust faulting, are still undetermined. It is 
believed that the detailed study of the surrounding areas, now 
under way, will clear up much that is now in doubt. The evidence 
available from this particular region will be discussed further 
along. 

There are a number of outcrops of the quartz schist in the 
area north of Morris and south of the tunnel line and again along 



^ Manual of the Geology of Connecticut. Conn. Geol. and Nat. Hist. Survey, Bull. 6, 
pp. 96-100, Hartford, 1906. 

2 Joseph Barrell, unpublished typewritten manuscript. 



Cf?OSS SECTION THROUGH TUNNEL LINE 



^ SS/^'ZZ'E- 



S35''46'£ 



Scale 
Vertical I" = 500' 
Horizontal l"= 2500' 



set" soe 




LEGEND 

Pegmatite Dikes 
Granite Dikes 

Biotite Hornbhndite Dikes 
Dioriie Porphyry Dikes 

PT^A^ Mai 



Brookfield Diorite 

Hartland Schist 
Berkshire Schist 



IRTTT] Gneis^ic 

I I Quarf z. + Mica Schist 

—^QuartZfte, Hornblende _ 



\ Muscovite, Garnet Schist 



Profile Map of Tunnel 
Bull. 40, Conn. Geol. & Nat. Hist. Survey 



No. 40] GEOLOGY OF SHEPAUG TUNNEL 21 

the main highway west from Morris to Lakeside, south of Bantam 
Lake. The outcrops of the latter set are intersected across the 
strike of the foHation by the road cuts and show their quartzite 
character but, if examined along the foliation planes, they closely 
resemble the mica schist type. It is apparently this series of 
outcrops coupled with several similar ones occurring near Bantam 
village and at 'The Jams" in the Bantam River, both north of 
Bantam Lake, that caused the area of Poughquag quartzite under- 
lying Bantam Lake and stretching to the south of it to be placed 
on the Preliminary Geological Map. The exposures underground 
show that the quartz schist south of the lake is a part of the Hart- 
land series and that that to the north represents fragments of the 
Hartland included in and metamorphosed by the diorite to a 
greater degree than the rest of the formation. 

In its first 6500 feet west from the outfall end, the tunnel cuts 
a monotonous repetition of quartz and mica schist diversified only 
by the prevalence of first one and then the other type and by the 
varying number of intrusions of granite and pegmatite. 

The mica schists are uniformly fine grained with smooth shiny 
surfaces and a micaceous luster. There is little fine crumpling 
and, where the rock is entirely free from injected igneous matter, 
it has almost the luster of a phyllite. Under the microscope this 
rock appears as an aggregate of biotite, muscovite, and quartz with 
subsidiary cloudy plagioclase, rare, rounded grains of apatite and 
variable amounts of pyrite. The proportion of biotite to mus- 
covite varies and quartz ranges from less than one-half the volume 
of the rock in the true mica schist to more than seventy per cent 
in the quartz schist. The latter has the same mineral composition 
as the mica schist except for the greater amount of quartz. 

The foliation of both types is due to the development of discon- 
tinuous bands of orientated mica laths. The space between these 
bands is filled by medium-grained quartz partly elongated parallel 
to the mica and partly in smaller equidimensional grains. The 
texture is crystalloblastic (Plate vi a). There is no sign of 
granulation but there is an occasional slight tendency for the mica 
to be wrapped around the larger elongated quartz crystals. 

This section of the schist has been cut by many pegmatite dikes 
and a lesser quantity of granite dikes and quartz veins. It is 
generally true that the intrusives parallel the foliation but some 
intersect it and all lack the foliation characteristic of the other 
rocks so that they must date from near the end of the period of 
folding or subsequent to it. The igneous rocks inject the schist on 
a small scale as well and locally turn it into a coarse-grained gneiss. 

The next one thousand feet of the tunnel pass through an 
interesting series of quartzites and sericite, hornblende, and garnet 
schists. The first variant to be encountered is a ten-foot bed of 
soft, white, lustrous muscovite schist. It differs from the normal 
mica schist, when examined under the microscope, only by the 



2 2 CONNECTICUT GEOL. AND NAT. HIST. SURVEY [BulL 

development of a greater amount of muscovite, almost complete 
absence of biotite, and the restriction of the quartz to a few layers. 
One hundred and two hundred feet beyond here there occur a 
fifteen-foot and a forty-foot bed of grayish white quartzite with 
very little banding. This is composed of eighty per cent quartz 
in grains with rather plain edges and mosaic texture, fifteen per 
cent clinozoisite, a little magnetite and colorless amphibole. 

This is followed by a series of garnet, hornblende and sericite 
schists about one hundred and fift}^ feet thick. The first is a 
coarsely crystalline, massive mixture of andesine, quartz, stauro- 
lite, unorientated muscovite and biotite, and rare garnets. Certain 
layers in this rock are composed of large, well-crystallized garnets 
containing inclusions of quartz and magnetite and altering to 
chlorite and some epidote. These are set in a ground mass of 
plagioclase, quartz and chloritized mica. Next follows a thirty- 
foot bed. of dark green hornblende schist speckled with pink garnet 
crystals a few millimeters in diameter. This rock is composed 
practically entirely of a fibrous green hornblende in short irregular 
laths and in aggregates of many crystals, and quartz. Rare grains 
of apatite and a little magnetite and plagioclase are seen through- 
out. The small equidimensional garnets cut irregularly across the 
foliation. This is followed by a twenty-foot bed of dark green 
hornblende schist without any garnets and with a greater propor- 
tion of iron oxide. The last of this series is a muscovite schist 
full of pinkish garnets and lesser amounts of titanite that give it 
a rough gneissoid apoearance. 

The next few hundred feet of the tunnel contain a few more 
bands of white muscovite schist from five to ten feet thick fol- 
lowed by two thousand feet of quartz and mica schist exactly like 
the first part. From there to a point within five hundred feet of 
the eastern corner in the tunnel the rock alternates between a dark 
green, fine-grained hornblende or hornblende mica schist and a 
sandy mica schist (Plate v b). From there to the contact between 
the Hartland and the Brookfield diorite, one hundred ninety-five 
feet northwest of the corner, the schist returns to its normal alter- 
nation of quartz and mica types. These persist right up to the 
contact where considerable black tourmaline, garnet, and staurolite 
are developed in the otherwise normal mica schist. The tourma- 
line alone of these minerals is not to be found in many parts of 
the rock and may represent additions from the diorite magma 
intruded into the schist. 

STRUCTURE 

Throughout the length of the Hartland section exposed in the 
tunnel, the dip is invariably to the west and the strike east ot 
north. Readings on the dip show a gradual increase from twenty- 
five degrees west at the contact to fifty-four degrees west at the 
portal with no great variation at any one point. The strike veers. 



No. 40] GEOLOGY OF SHEPAUG TUNNEL 23 

from north forty-five degrees east near the diorite, where it 
appears to parallel the contact, to a maximum of north seventy- 
five degrees east just west of the central portion and then swings 
irregularly back to north two degrees east at the portal. A short 
tunnel, 1635 feet long, drilled under the southern extension of 
Guernsey Hill one half a mile east of the outfall of the seven-mile 
tunnel (see map facing page 16), exposes a section with the 
dip averaging forty-five degrees west but with a strike of north 
ten deg^rees west. The rock here exposed is a repetition of quartz 
and mica schist. 

Outcrops of the Hartland schist are rare in the area mapped. 
In the hills east and northeast of Litchfield village there are a good 
many surface exposures of coarsely crystalline garnetiferous mica 
schist with a north-south strike and a dip west of vertical, while 
south and southeast of Bantam Lake there are a number of out- 
crops of fine-grained mica and quartz schist that strike from north 
seventy to north eighty east and dip northwest. At the southwest 
corner of the area near Mount Rat the Hartland — a lustrous, some- 
what sandy, fine-grained mica schist — forms a number of irregular 
re-entrants into an intruded mass of hornblende gneiss. The 
strike is nearly east-west and the dip north. 

It can be seen from this that the surface exposures give no more 
idea of the amount of folding that may have taken place than does 
the underground section. Either the beds compose one thick series 
all tilted one way or a series of overturned folds with isoclinal dip 
planed oflf by erosion and intersected by the tunnel far from the 
ends of the folds so that the dip of the original strata and the 
schistosity coincide. If the first be true, a series of immense thick- 
ness is present, more than eight thousand feet for the tunnel sec- 
tion alone, and that is but a small part of the whole. In consider- 
ing the second case it is true that any amount of repetition could 
be present in the main tunnel and in the short east section without 
changing the endless sequence of quartz and mica schist inter- 
sected by dikes of pegmatite. A consideration of the great thick- 
ness required by the first assumption is in itself enough to make 
repetition by folding almost a certainty. The amount of such 
repetition cannot be determined but we can at least assign a 
minimum thickness to the series. The sequence of sericite, horn- 
blende and garnet schists described previously and located near 
the central part of the main tunnel represents an easily recognized 
sequence which assuredly is not repeated in a linear distance of a 
little under two miles. With an average dip of forty degrees the 
thickness of the formation in this distance is 6500 feet, and if the 
telltale series were to come in immediately beyond the exposed 
area, the thickness of the formation without repetition of this 
series would be 3250 feet. 



24 CONNECTICUT GEOL. AND NAT. HIST. SURVEY [Bull. 

FAULTS 

There are a number of faults exposed in the underground 
section. Most of them are small normal faults with a relatively 
flat westerly dip. Only in one instance could an exact measure 
of the throw be made. Two vertical faults with the downthrow 
block on the west cause the repetition of two narrow calcareous 
bands of the schist with a combined throw of one hundred seventy 
feet. The strike of all these small faults averages nearly north- 
south. 

About one mile east of the eastern corner in the tunnel there is 
a fault of some magnitude. It strikes north sixty-four degrees 
east and dips twenty-four degrees north. Several feet of clay 
gouge accompany the fault and the foot wall rock is badly shattered 
for a distance of nearly one hundred feet. Due to the fractured 
character of the rock, it is impossible to determine the direction 
of the throw. There is no surface expression of the line of 
weakness nor can the fault affect the calculation of the minimum 
thickness of the schist given above since it lies to the west of 
the area considered. 



METAMORPHISM OF THE HARTLAND SCHIST 

The Hartland schist, in common with the other rocks of the 
region, has undergone a rather complicated set of changes. An 
original series of normal sedimentary strata made up of sandstone, 
shale, and relatively rare calcareous layers was so compressed by 
forces acting in a general east- west direction that the beds were 
greatly folded and overturned over considerable areas. Intrusions 
of granite on a regional scale accompanied the folding both as 
stocks several miles in diameter and as dikes and fine injections 
of granite and pegmatite. The stocks are in part strongly gneis- 
soid with a cataclastic texture showing that they preceded some of 
the folding, but the dikes, probably later offshoots from the same 
magma, show no sign of mashing. 

The schist is completely recrystallized and, in general, at least 
throughout the area here discussed, the foliation is parallel wath 
the original bedding. There is no granulation of the minerals 
and no suggestion of straining after the crystalloblastic texture 
developed. 

The area of Hartland schist covered by this report is entirely 
free from large granitic intrusions. To the east of this section 
the Thomaston granite and the pegmatite dikes form a large pro- 
portion of the surface outcrops and the schist is very thoroughly 
cut up and intimately penetrated by the igneous rocks. The 
granites nearly give out in the tunnel region but the pegmatites 
persist in great numbers and locally penetrate the schist to such 
an extent as to form a migmatite. 

A more complete study of the whole Hartland schist is needed 



No. 40] GEOLOGY OF SHEPAUG TUNNEL 25 

in order fully to appreciate the varying effect of igneous impreg- 
nation and injection upon the rock. The sandy, micaceous, and 
garnetiferous types with crystalloblastic texture far from any 
intrusives are certainly to be explained by dynamic metamorphism 
but the presence, at that time, of molten magmas underlying the 
area must have had an effect. The change from a simple recrys- 
tallized schist to a coarse injection gneiss that takes place in the 
neighborhood of the larger dikes and stocks of granite, is the 
effect of a cause that was doubtless at work to a lesser degree over 
a much greater area. 

One-eighth of a mile south of the outfall on a new road that 
skirts the valley into which the waters of the tunnel will flow, 
there is an exposure of closely folded schist and quartzite cut by 
pegmatite dikes in part earlier and in part later than the folding. 
These quartzite beds are worthy of note because they show a 
development of hornblende drawn out into pencils, small frag- 
ments of apatite, large skeletal crystals of garnet that appear to 
the naked eye as blurred, reddish brown spots on a white back- 
ground ; biotite, zircon, and a little magnetite. These minerals 
are best developed near the contact and, together with some granu- 
lation of the quartz, give the rock a distinct foliation. These 
minerals are due to the recrystallization of the impure parts of 
the original sandstone near the contacts. There are a number of 
narrow bands of similar rock in the tunnel. 

There is another type of alteration in the same rock in which 
hornblende and garnet are developed and the hornblende forms 
unorientated laths. This type is associated with the small peg- 
matite dikes that cut the quartzite and schist and is believed to be 
due to contact metamorphism by solutions emanating from the 
pegmatite. Some of the "pencils" of hornblende mentioned under 
the first type of alteration seem to be cut off abruptly or eaten into 
by quartz later than the recrystallization. Veins or irregular 
patches of crystalline calcite are common in certain parts of the 
quartzite. 

Two narrow calcareous beds in the short tunnel under the 
southern end of Guernsey Ridge represent a third type of alter- 
ation. They are composed of granular quartz, hornblende in 
unorientated blades, garnet, zoisite, titanite, muscovite, apatite, 
calcite, and considerable plagioclase with an index higher than 
that of quartz. None of these minerals are strained or crushed 
and the rock appears to be a mixed type — an impure limestone 
layer recrystallized and then penetrated by quartz and plagio- 
clase. There are no large dikes in the neighborhood so that the 
solutions must have traveled far and performed a selective 
replacement. 

The part that such impregnations and replacements have played 
in the total metamorphism of the area here under discussion is 
relatively slight, but it is believed that the neighboring areas, 



2 6 CONNECTICUT GEOL. AND NAT. HIST. SURVEY [BulL 

where intrusions are common, will show a greater proportion of 
such changes. 

The Berkshire Schist 

The Berkshire schist is a widespread formation in northwestern 
Connecticut and extends north into Massachusetts and southwest 
into New York. It varies considerably in its mineralogy and in 
the amount of metamorphism that it has undergone. The Berk- 
shire that extends into this map area is the same general type as 
that which forms Canaan Mountain — i. e., a coarse quartz, biotite 
schist with locally sufficient feldspar to be a gneiss.^ It is cut off 
from the Canaan Mountain mass in the north by a narrow belt of 
gneisses belonging to the Becket formation but is almost certainly 
a continuation of the Canaan Mountain rock. It is intruded by 
a large stock of Thomaston granite gneiss in the northwest corner 
of this area and is cut by many dikes of pegmatite. 

The areal distribution of the formation as mapped in the present 
report dififers considerably from that on the former map.^ The 
whole region about the Shepaug River west of the Brookfield 
diorite and north of Mount Tom is mapped as Berkshire, and the 
Becket, shown here on the former map, is omitted altogether. The 
first three thousand feet of the tunnel pass through a contorted, 
variable mica gneiss and open up a section not hitherto observable. 
Reasons are given below for regarding this rock as a part of the 
Berkshire formation, though such an assignment is certainly sub- 
ject to change when a more detailed study of that whole formation 
is completed. 

The Becket gneiss as originally mapped and described^ includes 
a great variety of metamorphic rocks in part originally igneous, 
in part sedimentary. Some parts are undoubtedly pre-Cambrian 
and some are of questionable age. The writer has begun to remap 
those areas and finds the following three main types: i. The 
Becket granite gneiss typified by the slightly gneissoid rock at 
Becket, Massachusetts, and Norfolk, Connecticut.* This is a 
white or grey quartz, microcline, oligoclase, biotite and (or) 
muscovite granite grading into a strongly gneissoid type with a 
cataclastic texture. 2. A paragneiss consisting of the Becket 
injected into some pre-existing biotite schist series. 3. An older 
series of metamorphosed sediments — the Hinsdale gneiss of B. K. 
Emerson^ made up of quartzite, altered limestone layers, and a 
siliceous biotite gneiss. The gneiss is very variable but is charac- 
terized by large amounts of microcline, dark brown biotite with 



1 See bottom of page 17 of this report. 

2 Preliminary Geological Map of Connecticut, H, E. Gregory and H. H. Robinson. 

3 Manual of the Geology of Connecticut, W. N. Rice and H. E. Gregory, Conn. Geol. 
and Nat. Hist. Survey Bull. No. 6, page 93, and Preliminary Geological Map of 
Connecticut by H. E. Gregory and H. H. Robinson. 

* Geology of Massachusetts and Rhode Island, B. K. Emerson, U.S.G.S. Bull. 597, 
pp. 154-155, 1917- 
5 Op. cit., page 10. 



No. 40] GEOLOGY OF SHEPAUG TUNNEL 27 

bent or broken lamellae, quartz with sutured boundaries and 
undulatory extinction, and considerable sillimanite. Apatite and 
garnet may be present. 

The Berkshire schist of the eastern belt described above and 
exclusive of the tunnel section is a very variable rock, but it may 
be characterized as a biotite schist or gneiss containing much 
quartz and up to ten per cent of oligoclase. Apatite is always 
present as small rounded grains and both garnet and staurolite are 
commonly formed. The biotite is frequently bent and where most 
disturbed sillimanite has formed and the quartz is partially granu- 
lated. This rock is intruded and injected by variable numbers of 
pegmatites and, in the Canaan Mountain section, is full of irregular 
knots of feldspar and garnet. 

The rock exposed in the first three thousand feet of the tunnel 
is a highly contorted biotite gneiss containing much quartz and 
oligoclase. Apatite, garnet and sillimanite may be present. The 
biotite lamellae are frequently warped but the quartz is only 
rarely granulated. These three thousand feet contain more than 
six hundred feet of pegmatite exclusive of the dikes only a few 
inches wide and the thin layers interlaminated with the schist. 

It is evident, therefore, that this rock does not resemble the 
Hinsdale gneiss. It contains no microcline and lacks the quartzite 
and metamorphosed limestone bands. On the other hand, its 
microscopic resemblance to the Berkshire is very striking and, 
bearing in mind what a variable formation the Berkshire is, 
there appears to be no reason for establishing a new series here. 
It is tentatively regarded, then, as a representative of the eastern 
belt of the Berkshire schist somewhat more thoroughly cut up by 
pegmatites than most of that rock. 

The strike of the foliation in the tunnel varies between north 
twenty and north thirty degrees east. The dip is prevailingly 
west at an angle of eighty degrees or more, though it occasionally 
flattens to forty-five degrees west, or stands vertical, or is very 
slightly overturned towards the east. Pegmatite dikes cut the 
schist at all angles and have very irregular contacts. In large 
part they lie parallel to the foliation but even then their bound- 
aries are irregular (Plate iv). A pegmatite may cut across 
several layers of schist as a fine dike only to spread out as a large 
bulb some distance from the main mass. This igneous or aqueo- 
igneous material has not replaced the schist to any noticeable 
extent but has confined its activity to an injection in fine layers 
and intrusion on a larger scale. 

There is one pegmatite two hundred and fifty feet thick that 
outcrops at the surface as well as underground. For the most 
part these dikes are composed of quartz, white microcline, albite 
and garnet, and exhibit no foliation, but there is one dike two 
hundred feet wide made up of pink microcline, quartz, some 
magnetite, garnet, and very little green pleochroic biotite, and 



2 8 CONNECTICUT GEOL. AND NAT. HIST. SURVEY [Bull. 

muscovite. It exhibits a coarse banding parallel to that of the 
wall rock. 

The contact between the Berkshire schist and the Brookfield 
diorite is very irregular. Diorite dikes have penetrated the schist 
several hundred feet from the contact and thick bands of the 
schist are included within the igneous rock but no intimate mixing 
of the two formations has taken place. 

It is impossible to draw conclusions concerning the structure 
and metamorphism of the Berkshire schist as a whole from the 
small section here described. Certain characteristics may be 
pointed out, however, that serve to distinguish it from the Hart- 
land schist with which it comes in contact both north and south 
of the tunnel. In the first place, there is no constant relation 
between the foliation and the former bedding planes. The folia- 
tion is due to coarse bands of oligoclase (in some cases albite) 
and quartz, rarely somewhat granulated, alternating with relatively 
thin layers of crumpled and strained biotite and much finer grained 
quartz. It lacks the simple crystalloblastic texture of the Hart- 
land schist. The rock was thoroughly recrystallized and injected 
in fine bands by quartz and feldspar, after which a slight move- 
ment gave it an incipient cataclastic texture and bent and folded 
the biotite laths that had formed in response to the first meta- 
morphism (see Plate vi b). 

Due to the similarity of various parts of this rock, the lack of 
any sign of original bedding and the number and size of the dikes 
that cut it, it is impossible even to estimate the thickness of the 
series. 

The Brookfield Diorite 

The Brookfield diorite forms a nearly circular mass in the center 
of the area described and separates the Hartland schist on the 
east from the Berkshire schist on the west. The tunnel passes 
through this formation from west to east and serves to locate its 
boundaries in this direction with great accuracy. The line of bore 
holes bored along the course originally proposed for the tunnel 
across the broad upper end of Bantam Lake served to locate the 
Brookfield-Hartland contact under Cranberry Pond and swamp. 
The contact in the tunnel itself is a little northwest of the angle 
near the base of Marsh's Point, and the western contact with 
the Berkshire is located almost beneath the highest point of the 
first hill in the tunnel line east of the Shepaug River. 

Little Mount Tom, near the southwest corner of the map, is 
now known to be composed of the same hornblende gneiss as 
Mount Tom (see next chapter), so that the diorite boundary 
swings along the northeast foot of both those hills. The rest of 
the boundary is taken from the Preliminary Geological Map of 
Connecticut. The contact is everywhere covered and no reason 
is known to change it. 



No. 40] GEOLOGY OF SHEPAUG TUNNEL 29 

A smaller mass of the same diorite lies immediately south of 
East Morris and extends north onto the southerly edge of this 
map in the midst of the Hartland schist. It is about one mile 
long and one-quarter of a mile wide. 

The Brookfield diorite is not a single simple intrusive but repre- 
sents a number of different textural and mineralogical types. 
The characteristic diorite from which the formation was named 
is a green and white, mottled, medium-grained rock with a granitic 
texture (Plates ii b and vii a). It is essentially a hornblende, 
biotite, andesine or oligoclase diorite with variable but usually large 
amounts of apatite and titanite, occasionally some diopside and 
small amounts of quartz. There are two variants of this massive 
type, one a light -colored quartz diorite composed of quartz, biotite 
and andesine, the other a fine-grained, granular, porphyritic diorite 
similar in composition to the first type described but with the 
addition of scattered andesine phenocrysts from one-eighth to 
one-quarter of an inch in length. There are recurrent masses of 
fine-grained, schistose diorite or coarse diorite gneiss throughout 
the tunnel that do not differ mineralogically from the granular 
textured types. The foliation is due to the development of more 
biotite, sometimes at the expense of the hornblende, with definite 
orientation and with the consequent formation of bands richer in 
hornblende and biotite, or in feldspar as the case may be ; and 
to some straining and bending of the biotite and plagioclase and 
granulation of the quartz when present. 

The strike of the banding in the foliated diorite parallels that 
of the surrounding schists as a general rule but veers toward the 
northwest both east and west of the northern angle in the tunnel. 
The trend of the intruded porphyry dikes and the inclusions of 
Hartland schist changes with the diorite and the dip swings to 
the northeast or east. This does not bear any relation to the trend 
of the diorite border since, before the Hartland schist is reached, 
the strike swings back to the northwest and the dip to the west, 
the normal dip and strike in the area, parallel with the foliation of 
the schist and nearly parallel with the contact. 

So far as can be determined from the surface outcrops, this 
change in strike and dip does not occur in the other formations 
but is confined to the diorite and its inclusions. 

Dikes of gneissoid, quartz monzonite porphyry from a few 
inches to twenty feet thick cut the diorite throughout its extent 
and outcrop at various places, such as on the tip of Dempsey's 
Point on the north shore of Bantam Lake. This rock is conspic- 
uous because of white or pinkish phenocrysts of microcline from 
one-quarter to more than three inches in length (Plate v a) set at 
all angles in a groundmass of quartz, potash feldspar, green biotite 
and andesine. Pyrite, apatite, and muscovite form the accessory 
minerals. The groundmass of the dikes usually possesses a rough 
gneissoid banding due to the segregation of the biotite into sepa- 



30 CONNECTICUT GEOL. AND NAT. HIST. SURVEY [Bull. 

rate layers and the granulation of much of the quartz, especially 
that surrounding the microcline phenocrysts and some crushing 
of the microcline itself. 

Still another vastly different type of dike rock occurs. That is 
a biotite hornblendite composed in large part of those two minerals 
together with some apatite, pyrrhotite and magnetite, a little color- 
less amphibole and, in one instance, monoclinic pyroxene, in 
another, a little andesine and quartz. In plane polarized light the 
hornblende is light green but shows strong pleochroism — blue- 
green parallel with Z and light yellow-green parallel with X with a 
maximum extinction angle of twenty-nine degrees. It frequently 
merges into a colorless, non-pleochroic am.phibole with a slightly 
lower extinction angle and birefringence. This is not a case of 
sharp zoning. The two usually blend irregularly with green at 
the center or are patchily distributed one within the other. The 
texture of this rock is massive and the biotite is commonly devel- 
oped along the prismatic cleavage planes of the hornblende. 
(Plate VII b.) 

Three small dikes of this type occur near the eastern edge of 
the diorite but the great majority are grouped around the central 
section of the tunnel just east and west of the Bantam River 
crossing. They all strike north to northeast and are between ten 
and two hundred feet thick. 

There is no identical rock that outcrops in this or in neighboring 
regions. The norites, gabbros, and related rocks of Mount Pros- 
pect^ approach it most closely. They are unmetamorphosed intru- 
sives younger than the main mass of the diorite and though they 
usually contain considerable monoclinic or orthorhombic pyroxene, 
some are nearly all hornblende and mica. 

There is some similarity, then, between the two groups, espe- 
cially since the biotite hornblendite dike in the tunnel nearest to 
Mount Prospect contains a good deal of monoclinic pyroxene, and 
pyrrhotite is a constant accessory in the dikes as well as being the 
cause of the long-abandoned nickel prospects on Mount Prospect 
itself. 

The complexity of types grouped here under the term Brookfield 
diorite is considerable and does not represent a simple sequence of 
intrusions. A hand specimen three by three inches Avill often 
show both coarse and fine-grained types with a good deal of dif- 
ference in the amount of feldspar present, and the coarse-grained 
diorite grades quickly but evenly into the fine-grained, granular 
type with small but distinct plagioclase phenocrysts. A certain 
amount of segregation or differentiation in place has occurred but 
that cannot explain all of the variations. The granodiorite and 
the microcline porphyry types are distinct dikes and, as was pointed 
out above, much of the diorite is rather strongly foliated. Those 



1 On Two New Occurrences of the "Cortland Series" of Rocks within the State of 
Connecticut. W. H. Hobbs, Fest. H. Rosenbusch, pp. 25-48, Stuttgart, 1906. 



No. 40] GEOLOGY OF SHEPAUG TUNNEL 3 1 

parts have no peripheral or other regular arrangement nor are 
they always marked off sharply from types with a granitic texture. 
The varying degree of foliation represented shows that these 
various parts were intruded at slightly different dates, ranging 
from before the end of the regional pressure till after the cessation 
of all metamorphism. 

The biotite-hornblendite dikes, like their supposed relatives on 
Mount Prospect, are unmetamorphosed. They were intruded late 
in the sequence and nearly always occur within a schistose area of 
diorite or between a schistose and a massive type. 

The Schist Inclusions in the Diorite 

The diorite contains a considerable number of inclusions of 
quartz and mica schist, mostly too small to be mapped on the scale 
employed, clearly related to the Hartland schist. These are most 
plentiful near the central part of the diorite and disappear entirely 
within a few thousand feet of the Brookfield-Berkshire contact 
on the west. As was mentioned before, the strike and dip of these 
included layers varies with that of the foliation in the diorite. 

The mineralogy of these inclusions is much the same as that of 
the rest of the Hartland series. Quartz, biotite, muscovite, some 
plagioclase, garnet, apatite, and pyrite are the common minerals. 
Rare titanite, sillimanite, calcite, and in some cases considerable 
diopside are the additional minerals not found in other parts of 
the schist. These bands represent the quartz and mica schist f acies 
of the Hartland only slightly changed chemically but with very 
different textures. In place of the simple recrystallization tex- 
tures seen before, we find cataclastic textures with a true mortar 
texture in some cases (Plate viii a) . In these the quartz is crushed 
around large and slightly strained feldspars, the biotite is bent 
around these more resistant masses and much sillimanite is formed 
in curved rods or bundles. In certain cases a good deal of graniti- 
zation of the inclusion had taken place before it was incorporated 
into the diorite and bands of quartz and orthoclase with a little 
micropegmatite alternate with quartz, biotite and sillimanite f oliae. 
Both of the bands show crushing. In one instance the schist 
inclusion is directly alongside a dike of rather gneissoid Thomaston 
granite and itself contains an unusual amount of quartz and some 
fresh microcline grains. 

The calcite that is found in most of these schists as well as in 
the diorite itself is very rarely if ever formed in place from the 
alteration of the plagioclase but is usually introduced along micro- 
scopic veins and faults. Only one case is known where the calcite 
is present in appreciable quantity as small irregular grains through- 
out the rock and that is in the quartz diopside schist at the entrance 
to the tunnel just west of the Bantam River crossing. Pyroxene 
forms ten per cent or more of this rock and quartz eighty to 



32 CONNECTICUT GEOL. AND NAT. HIST. SURVEY [Bull. 

eighty-five per cent with a very Httle muscovite, pyrite, plagioclase 
and calcite. 

Close to the western boundary of the diorite there are two areas 
of mica gneiss included within the main igneous mass. These are 
undoubtedly related to the Berkshire schist but exhibit a more 
advanced stage of crushing than that outside of the diorite. The 
texture is schistose — that is, they have been recrystallized along 
with the rest of the Berkshire — but the minerals so formed have 
suffered further deformation to a greater degree than those in the 
mass of the schist. The quartz is slightly to nearly completely 
granulated and the biotite is moulded around the more resistant 
garnet and plagioclase crystals. The difference in the degree of 
crushing is about the same as that between the Hartland schist 
and its representatives included within the diorite. 

The Mount Tom Hornblende Gneiss 

The three prominent hills in the southwest corner of the region, 
Mount Tom, Little Mount Tom, and Mount Rat, are composed 
of a dark green or green and white hornblende gneiss. The irreg- 
ular area occupied by this rock is two miles broad on the east, 
where it abuts against the Brookfield diorite, and projects in two 
long spurs to the southwest into the Hartland schist. The longest 
of these spurs is more than three miles long and forms the ridge 
of Mount Rat. 

The gneiss is composed chiefly of green hornblende and andesine 
with smaller amounts of quartz and with titanite and magnetite 
forming rare accessories. The texture is nearly everywhere 
strongly gneissoid though it is more massive near the center of 
the area than along the borders. The foliation is due to the very 
complete granulation of the plagioclase and the parallel orientation 
of the hornblende laths. Quartz is present in considerable quanti- 
ties and always in much larger individual grains than the plagio- 
clase (Plate VIII b). Some of it occurs in lenticular groups of 
grains which strongly suggest a certain amount of granulation but 
much less than the pulverized andesine. The hornblende laths 
sometimes end in fine rods that pass out into the ground-up plagio- 
clase. They are only in part crushed and do not seem to show as 
great effects of pressure as it would seem should accompany such 
complete crushing of the feldspar. The rock has about the same 
composition as the quartz-bearing types of the Brookfield diorite, 
with a little more hornblende, but it must not be confused with 
the gneissic derivatives of the diorite. Those have a cataclastic 
texture developed by pressure that affected an already solidified 
rock. The Mount Tom gneiss, on the other hand, has a proto- 
clastic texture developed through pressure during solidification 
after the plagioclase had crystallized but before the quartz was 
formed. The fine, unbroken rods of hornblende appear to show 



No. 40] GEOLOGY OF SHEPAUG TUNNEL 33 

that the recrystallization of that mineral had just begun when the 
pressure ceased. 

On the southwest slope of Mount Rat, northeast of the road that 
crosses between the two high knobs, the hornblende gneiss is 
exposed in a field as a series of dikes or sills cutting a silvery 
white, fine-grained type of the Hartland schist. The foliation of 
the two rocks is parallel and strikes nearly east and west. One 
of the intrusions has a very irregular contact zone with fragments 
of the schist included in the gneiss and a light green epidote schist 
developed in nodules along its edge. The microscope shows that 
these nodules are similar to the main gneiss with the addition of 
large amounts of epidote. 

The protoclastic texture and the igneous contact of the gneiss 
are of particular interest since they prove the igneous character 
of the rock and establish something with which to compare the 
many other hornblende gneisses among the metamorphic rocks of 
western Connecticut. There are hornblende gneisses in the Berk- 
shire schist and in the areas now mapped as Becket gneiss that 
resemble this rock very closely. There are others in the Becket 
and in the Hartland schist that have been formed out of original 
sediments. 

The Thomaston Granite Gneiss 

The Thomaston granite gneiss is an intrusive rock that is rather 
widely developed in the western upland of Connecticut, particularly 
in the central and southern parts. The texture varies from that 
of a massive granite with no sign of foliation to a decidedly 
gneissoid type with a secondary development of mica and con- 
siderable granulation of the quartz. The least metamorphosed 
part, as at the Plymouth quarry at Thomaston, was described in 
the Manual of the Geology of Connecticut, page 109, as follows: 
.... ''the rock is remarkably white in color, has a medium grain, 
and is flecked by numerous small scales of mica (biotite)- The 
v/hite base of the rock is made up of about equal parts of a white 
feldspar (microcline) and quartz. Locally, as in the Wilton area, 
it is distinctly porphyritic with phenocrysts of microcline which 
sometimes reach one-half an inch in length." 

Only one considerable mass of the Thomaston granite gneiss 
occurs in this map area. It intrudes the Berkshire schist in the 
northwest corner of the area and projects some distance beyond 
it to the north and northwest. It is a gneissoid quartz, microcline, 
muscovite, and biotite granite with considerable oligoclase, micro- 
pegmatite and some apatite. The biotite is dark brown with 
strong pleochroic halos around minute zircons. The texture is 
usually cataclastic and the foliation is due to the parallel orientation 
of the mica flakes and the granulation of the quartz grains. 

There are two large dikes of exactly this same character cutting 
the Brookfield diorite just west of the Bantam River opening ia 



34 



CONNECTICUT GEOL. AND NAT. HIST. SURVEY 



[Bull. 



a * 



4) 

CO - 



^5 
I 

N 

C o 
o 

3: 



o 

u 

u 

I 

6 



No. 40] GEOLOGY OF SHEPAUG TUNNEL 35 

the tunnel. The remaining granite dikes that occur in the tunnel — • 
to some extent in the diorite but to a much greater degree in the 
Hartland schist — are granitic textured rocks that have the same 
composition as the gneiss noted above but lack its foliation. Great 
quantities of pegmatite dikes, large and small, cut the Brookfield 
diorite and the Berkshire and Hartland schists throughout the 
tunnel. Some of these dikes show a distinct foliation and small 
ones are apt to be folded with the schists, but the majority are 
massive and cut across the foliation planes of the older rocks. 



Buried Surface Features Exposed by the Tunnel and the 
Diamond Drill Holes 

It is not the purpose of this report to describe the glacial 
phenomena of the region in detail but certain features that have 
been exposed to view by the tunnel excavation or by the diamond 
drill holes that preceded the excavation can properly be included. 



pre-pleistocene weathering preserved south of mount 

prospect 

It is generally true in this region, as would be expected in a 
recently glaciated area, that the rock underlying the rather thin 
cover of till has undergone very little weathering since the products 
of pre-Pleistocene decay were swept away by the advancing ice. 
There is one notable exception to this rule immediately west of 
the peat bog that lies in the path of the tunnel fifteen hundred 
and sixty feet west of the Bantam River crossing. For a distance 
of nearly two thousand feet the tunnel was driven through soft, 
rotten rock that made considerable trouble for the engineers since 
it necessitated continual timbering. A number of small faults 
occur in this part and both the diorite and biotite-hornblendite are 
crushed and slickenslided in several places, but these faults are 
neither large enough nor common enough to be the direct cause 
of the weakness of the rock, though they may have helped to 
cause the unusual depth of decay. This area of deep pre-glacial 
weathering was apparently partly protected from glacial erosion 
by the higher lands to the north and some part of the weathered 
rock was preserved. 

THE PRE-GLACIAL SURFACE UNDER THE NORTH END OF BANTAM 

LAKE 

The diamond drill holes that were bored into the bed of the 
lake to determine the thickness of the rock cover above the pro- 
posed tunnel line directly across the northern part of the lake 
showed a surprising depth of sand, gravel and heterogeneous 



36 CONNECTICUT GEOL. AND NAT. HIST. SURVEY [Bull. 

boulder beds lying below the lake silts (Fig. 3). The proposed 
tunnel would have passed out of the solid rock into the glacial till 
and a change in plan was necessitated. Borings across the nar- 
rows between Dempsey's Point and Marsh's Point showed a safe 
thickness of rock above the tunnel but uncovered a gorge between 
these two headlands (Profile Map — central part). Evidently the 
pre-Pleistocene Bantam River flowed through a broad valley to 
the north and a relatively restricted gorge under the present 
narrows of the lake. The difference in the level of the bed rock 
must be explained by depth of weathering or glacial scour or both. 
South of the lake a seemingly trivial glacial divide blocked off the 
original course of the stream and caused it to flow out of Bantam 
Lake to the north within a short distance from where it enters the 
lake. 

The original line of bore holes also shows that the long north- 
south ridge between Bantam Lake and Cranberry swamp has no 
corresponding rock ridge beneath it. The hill is composed entirely 
of glacial debris and the old land surface rose only slightly from 
the river's bank to fall again beneath the present swamp, then rose 
steeply to the east to form high rocky ridges. 

Marsh's Point is also composed of glacial till though the rock 
surface rises nearer to the present surface than in the first case. 

The extensive sand plain to the north of the northern expansion 
of Bantam Lake lies at about the same level as the swamp and only 
a few feet above the lake itself. The bore holes run south of this 
plain so that the depth at which the bed rock lies is not known. 

Summary 

It may be stated in conclusion that this area was chosen for a 
special report because of the construction of the tunnel that 
exposed -niany features otherwise hidden from view. To be 
sure, it is a critical area because the two schist series come 
together, though, unluckily, an actual contact has not been found ; 
but it is a difficult area to treat as an entity separate from the rest 
of the western upland because it touches many problems that 
cannot be solved in the area itself. The details are here presented 
with full recognition that they represent only a part of a vastly 
greater whole, but with the conviction also that they will aid in 
the solution of the problems connected with them. 

The tunnel section and the examination of the outcrops in the 
surrounding region have caused a number of changes on the 
areal map. First, the Poughquag quartzite shown on the former 
map around Bantam Lake is not present at all, but there are 
many outcroppings of a quartz schist that forms a part of the 
Hartland series. Second, the Becket gneiss formerly mapped 
along the Shepaug River at the entrance of the tunnel is also 
non-existent. That area is now tentatively placed as a part of 



No. 40] GEOLOGY OF SHEPAUG TUNNEL 37 

the Berkshire schist. Finally, the rock forming Mount Tom and 
the neighboring hills is not a true amphibolite but a hornblende 
gneiss with a protoclastic texture, and Little Mount Tom is 
composed of the same rock and not, as previously mapped, of 
Brookfield diorite. 

Besides these definite changes the areal distribution of certain 
formations has been altered considerably ; the boundaries between 
the Brookfield diorite and the neighboring schists have been located 
more accurately ; the diorite itself has been shown to be a composite 
of many closely related intrusions, and the Berkshire schist to be 
considerably older than the Hartland. 

Bibliography 

1. Observation of the Minerals Connected with the Gneiss Ranges 
of Litchfield, Conn. J. P. Brace, Am. Jour. Sci., (i) i, 351-355- 
1819. 

2. Sketches of a Tour in the Counties of New Haven and Litchfield 
in Connecticut, with Notices of the Geology, Mineralogy, and 
Scenery. B. Silliman, Am. Jour. Sci.. (i) 2, 201-235, 1820. 

3. Report on the Geology of the State of Connecticut. J. G. 
Percival, 1842. 

4. On the Southward Ending of a Great Synclinal in the Taconic 
Range. J. D. Dana, Am. Jour. Sci., (3) 28, 268-276, 1884. 

5. Archaean Limestone and Other Rocks in Norfolk, Connecticut. 
J. D. Dana, Am. Jour. Sci., (3) 39, 321, 1890. 

6. The Geologic Structure of the Housatonic Valley Lying East of 
Mount Washington. W. H. Hobbs, Jour. Geol., i, 780-802, 1893. 

7. Geology of the Green Mountains in Massachusetts. R. Pum- 
pelly, T. N. Dale, J. E. V/olff, U. S. Geol. Surv. Mon. 23, 1894. 

8. Notes on the Geology of Southwestern New England. W. H. 
Hobbs, Jour. Geol. 5, I75-I77, 1897. 

9. Geology of Old Hampshire County, Massachusetts. B. K. 
Emerson, U. S. Geol. Surv. Mon. 29, 1898. 

ID. Geology of Eastern Berkshire County, Massachusetts. B. K. 
Emerson, U. S. Geol. Surv. Bull. 159, 1899. 

11. The Geologic Structure of the Southwestern New England 
Region. W. H. Hobbs, Am. Jour, Sci., (4) 15, 437-446, 1903. 

12. On Two New Occurrences of the "Cortland Series" of Rock5 
within the State of Connecticut. W. H. Hobbs, Festschrift v. 
H. Rosenbusch, 25-48, Stuttgart, 1905. 

13. Manual of the Geology of Connecticut. W. N. Rice and H. E. 
Gregory, Conn. Geol. and Nat. Hist. Surv. Bull. 6, 1906. 

14. Preliminary Geological Map of Connecticut. H. E. Gregory and 
H. H. Robinson, Conn. Geol. and Nat. Hist. Surv. Bull. 7, 1907. 

15. Structural and Stratigraphic Features of the Basal Gneisses of 
the Highlands. C. P. Berkey, N. Y. State Mus. Bull. 107 (Geol. 
12) 361-368, 1907. 

16. The Granites of Connecticut. T. Nelson Dale and Herbert E. 
Gregory, U. S. Geol. Surv. Bull. 484, 191 1. 

17. The Geology of the Poughkeepsie Quadrangle. C. E. Gordon, 
N. Y. State Mus. Bull. 492, 191 1. 

18. Sulphide Bearing Rocks from Litchfield, Connecticut. Emest 
Howe, Ec. Geol. X, No. 4, June, 1915. 

19. Geology of Massachusetts and Rhode Island. B. K. Emerson^ 
U. S. Geol. Surv. Bull. 597, 1917. 



38 CONNECTICUT GEOL. AND NAT. HIST. SURVEY 

20. Geology of the West Point Quadrangle. C. P. Berkey and 
Marion Rice, N. Y. State Mus. Bull. 225-226, 1921. 

21. Relations of Subjacent Igneous Invasion to Regional Metamor- 
phism. J. Barrel!, Am. Jour. Sci., 5th Series, No. i, 1-19; No. 2, 
174-186; No. 3, 255-267, 1921. 

'22. The Lime Belt of Massachusetts and Part of Eastern New York 
and Western Connecticut, T. N. Dale, U. S. Geol. Surv. Bull. 
744, 1923. 



PLATE I. 




View looking up the Shepaug River Valley, soon to be turned into 
a reservoir. Tunnel entrance to the right of the shacks. Photo- 
graph by B. H. Walden. 




b. View looking into entrance of tunnel from across the Shepaug River, 
along the line of the proposed dam. 



PLATE II. 




a. View looking down the Shepaug River from below the site of the 
proposed dam. Part of the dump from the tunnel excavation is 
shown at the left. 




b. View showing the massive character of the Brookfield diorite at the 
entrance to the tunnel east of the Bantam River crossing. 



PLATE III. 




View looking across the narrows of Bantam Lake from Dempsey's 
Point to Marsh's Point. The tunnel passes under the lake between 
these points. 




Valley of the West Branch of the Naugatuck River above the 
present Morris Reservoir and just below the tunnel outfall, where 
the waters of the Shepaug River will be brought through the 
tunnel and impounded. 



PLATE IV. 




Irregular contact between the Berkshire schist and a pegmatite dike 
in the tunnel, looo feet east of the tunnel entrance at the Shepaug 
River. Two drill holes are shown in the schist at the left. Photo- 
graph by B. H. Walden. 



PLATE V. 




Quartz monzonite porphyry dike cutting the massive diorite in the 
tunnel under Bantam Lake. Photograph by B. H. Walden. 




Pegmatite lenses parallel with the flat dipping foliation of the Hart- 
land mica schist, looo feet east of the southernmost corner in the 
tunnel. Photograph by B. H. Walden. 



PLATE VI. 




a. Hartland mica schist showing crystalloblastic texture. 
Crossed nicols x 25. 




Berkshire schist from west end of tunnel showing curved biotite 
flakes (B) and quartz (Q) partly granulated. An incipient 
cataclastic texture superimposed upon a crystalloblastic texture. 
Crossed nicols x 25. Photograph by D. Selchow. 




PLATE VII. 






i 




^■3 



"'^Si' 



a. Brookfield diorite near center of tunnel showing texture of crystalli- 
zation. (H) hornblende; (B) biotite; (P) plagioclase (mostly 
andesine). Plane polarized light x 40. 




b. Biotite hornblendite near center of tunnel showing texture of crys- 
tallization. (H) hornblende; (B) biotite; (T) colorless amphibole 
grading into the hornblende. Plane polarized light x 40. 



PLATE VIII 




Hartland schist included in Brookfield diorite showing large crystal 
of andesine, strained throughout and somewhat crushed along the 
edges and in a line through center ; granulated quartz, and biotite 
bent around the more resistant fragment. Shows mortar texture. 
Crossed nicols x 25. 




b. 



Mount Tom hornblende gneiss showing pulverized plagioclase (P), 
larger individuals of quartz (Q), and hornblende (H), projecting 
as fine needles into pulverized plagioclase. Protoclastic texture 
with beginning of recrystallization. Crossed nicols x 40. Photo- 
graph by D. Selchow. 



BULLETINS 

OF THE 

State Geological and Natural History Survey 
of Connecticut 



1. First Biennial Report of the Commissioners of the State 
Geological and Natural History Survey, 1903-1904; 18 pp., 23 
cm., 1904. 

2. A Preliminary Report on the Protozoa of the Fresh Waters 
of Connecticut : by Herbert William Conn, Ph.D. ; 69 pp., 34 pis., 
23 cm., 1905. (Out of print as a separate bulletin. To be obtained 
only in Vol. I, containing Bulletins i-^. Price $1.75 postpaid.) 

3. A Preliminary Report on the Hymeniales of Connecticut: 
by Edward Albert White, B.S. ; 81 pp., 40 pis., 23 cm., 1905. 
{Out of print as a separate bulletin. To be obtained only in Vol. 
I, containing Bulletins i-j. Price $1.75 postpaid.) 

4. The Clays and Clay Industries of Connecticut: by Gerald 
Francis Loughlin, S.B.; 121 pp., 13 pis., 23 cm., 1905. 

5. The Ustilagineae, or Smuts, of Connecticut: by George 
Perkins Clinton, S.D. ; 45 pp., 55 figs., 23 cm., 1905. 

6. Manual of the Geology of Connecticut: by William North 
Rice, Ph.D., LL.D., and Herbert Ernest Gregory, Ph.D. ; 273 pp., 
31 pis., 22 figs. (10 maps), 23 cm., 1906. (Out of print as a 
separate bulletin. To be obtained only in Vol. II, containing 
Bulletins 6-12. Price $2.7 5 postpaid.) 

7. Preliminary Geological Map of Connecticut: by Herbert 
Ernest Gregory, Ph.D., and Henry Hollister Robinson, Ph.D. ; 
39 pp., 2 maps (i in pocket), 23 cm., 1907. (Out of print as a 
separate bulletin. To be obtained only in Vol. II, containing 
Bulletins 6-12. Price $2.75, postpaid.) 

8. Bibliography of Connecticut Geology: by Herbert Ernest 
Gregory, Ph.D. ; 123 pp., 23 cm., 1907. 

9. Second Biennial Report of the Commissioners of the State 
Geological and Natural History Survey, 1905-1906; 23 pp., 23 cm., 
1906. 

10. A Preliminary Report on the Algae of the Fresh Waters 
of Connecticut: by Herbert WilHam Conn, Ph.D., and Lucia 
Washburn (Hazen) Webster, M.S. ; y% pp., 44 pis., 23 cm., 1908. 

11. The Bryophytes of Connecticut: by Alexander William 
Evans, Ph.D., and George Elwood Nichols, B.A. ; 203 pp., 23 cm., 
1908. 



12. Third Biennial Report of the Commissioners of the State 
Geological and Natural History Survey, 1907-1908; 30 pp., 23 
cm., 1908. 

13. The Lithology of Connecticut: by Joseph Barrell, Ph.D., 
and Gerald Francis Loughlin, Ph.D.; 207 pp., 6 tables, 23 cm., 
1910. 

14. Catalogue of the Flowering Plants and Ferns of Con- 
necticut Growing without Cultivation: by a Committee of the 
Connecticut Botanical Society consisting of Charles Burr Graves, 
A.B., M.D., Edwin Hubert Fames, M.D., Charles Humphrey 
Bissell, Luman Andrews, Edgar Burton Harger, Ph.B,, and 
Charles Alfred Weatherby, A.M. ; 569 pp., 23 cm., 1910. 

15. Second Report on the Hymeniales of Connecticut: by 
Edward Albert White, B.S. ; 70 pp., 28 pis., 23 cm., 1910. 

16. Guide to the Insects of Connecticut: prepared under the 
direction of Wilton Everett Britton, Ph.D. Part I. General 
Introduction: by Wilton Everett Britton, Ph.D. Part II. The 
Euplexoptera and Orthoptera of Connecticut: by Benjamin Hovey 
Walden, B.Agr. ; 169 pp., 11 pis., 16 figs, (i map), 23 cm., 1911. 

17. Fourth Biennial Report of the Commissioners of the State 
Geological and Natural History Survey, 1909-10; 31 pp., 23 cm., 
1910. 

18. Triassic Frshes of Connecticut: by Charles Rochester 
Eastman, Ph.D.; y% pp., 11 pis., 8 figs., 23 cm., 1911. 

19. Echinoderms of Connecticut: by Wesley Roswell Coe, 
Ph.D.; 152 pp., 32 pis., 29 figs., 23 cm., 1912. 

20. The Birds of Connecticut: by John Hall Sage, M.S., and 
Louis Bennett Bishop, M.D., assisted by Walter Parks BHss, 
M.A. ; 370 pp., 23 cm., 1913. 

21. Fifth Biennial Report of the Commissioners of the State 
Geological and Natural History Survey, 1911-1912; 27 pp., 23 
cm., 1912. 

22. Guide to the Insects of Connecticut: prepared under the 
direction of Wilton Everett Britton, Ph.D. Part HI. The 
Hymenoptera, or Wasp-like Insects, of Connecticut: by Henry 
Lorenz Viereck, with the collaboration of Alexander Dyer Mac- 
Gillivray, Ph.D., Charles Thomas Brues, M.S., William Morton 
Wheeler, Ph.D., and Sievert Allen Rohwer; 824 pp., 10 pis., 15 
figs., 23 cm., 1916. 

23. Central Connecticut in the Geologic Past: by Joseph 
Barrell, Ph.D.; 44 pp., 5 pis., 23 cm., 1915. 

24. Triassic Life of the Connecticut Valley: by Richard 
Swann Lull, Ph.D. ; 285 pp., 3 maps, 12 pis., 126 figs., 23 cm., 

1915. 

25. Sixth Biennial Report of the Commissioners of the State 
Geological and Natural History Survey, 1913-1914; 24 pp., 23 
cm., 1915. 



26. The Arthrostraca of Connecticut: by Beverly Waugh 
Kunkel, Ph.D. ; 261 pp., 84 figs., 23 cm., 1918. 

27. Seventh Biennial Report of the Commissioners of the 
State Geological and Natural History Survey, 1915-1916; 17 pp., 
23 cm., 1917. 

2S. Eighth Biennial Report of the Commissioners of the State 
Geological and Natural History Survey, 1917-1918; 21 pp., 23 
cm., 1919. 

29. The Quaternary Geology of the New Haven Region, 
Connecticut: by Freeman Ward, Ph.D.; 80 pp., 9 pis., 17 figs., 
23 cm., 1920. 

30. Drainage Modifications, and Glaciation in the Danbury 
Region, Connecticut : by Ruth Sawyer Harvey, Ph.D. ; 59 pp., 
5 pis., 10 figs., 23 cm., 1920. 

31. Check List of the Insects of Connecticut: by Wilton 
Everett Britton, Ph.D. ; 397 pp., 23 cm., 1920. 

32. Ninth Biennial Report of the Commissioners of the State 
Geological and Natural History Survey, 1919-1920; 18 pp., 23 
cm., 1920. 

33. Geology of the Stonington Region, Connecticut: by 
Laura Hatch Martin, Ph.D.; 70 pp., i map, 8 figs., 23 cm., 1925. 

34. Guide to the Insects of Connecticut: prepared under the 
direction of Wilton Everett Britton, Ph.D. Part IV. The 
Hemiptera or Sucking Insects of Connecticut : by Wilton Everett 
Britton, Ph.D., with the collaboration of James Francis Abbott, 
Ph.D., Arthur Challen Baker, Ph.D., Harry Gardner Barber, 
A.M., William Thompson Davis, Dwight Moore DeLong, Ph.D., 
William Delbert Funkhouser, Ph.D., Harry Hazelton Knight, 
Ph.D., Asa Chandler Maxson, Herbert Osborn, D.Sc, Howard 
Madison Parshley, Sc.D., Edith Marion Patch, Ph.D., Louis 
Agassiz Stearns, M.Sc, Jose Rollin de la Torre-Bueno, F.E.S., 
Edward Payson Van Duzee, Harley Frost Wilson, M.S. ; 807 pp., 
20 pis., 169 figs., 23 cm., 1923. 

35. Tenth and Eleventh Biennial Reports of the Commis- 
sioners of the State Geological and Natural History Survey, 1921- 
1924; 17 pp., 23 cm., 1924. 

36. The Uredinales or Rusts of Connecticut and Other New 
England States : by Willis Roberts Hunt, Ph.D. ; 198 pp., 2 figs., 
23 cm., 1926. 

37. Catalogue of the Lichens of Connecticut: by Alexander 
WilHam Evans, Ph.D., and Rose Meyrowitz, M.S. ; 56 pp., 23 
cm., 1926. 

38. Twelfth Biennial Report of the Commissioners of the State 
Geological and Natural History Survey, 1925-1926; 23 pp., i pi., 
23 cm., 1927. 

39. The Odonata or Dragonflies of Connecticut : by Philip 
Garman, Ph.D.; 331 pp., 22 pis., 6y figs., 23 cm., 1927. 



40. The Geology of the Shepaug Aqueduct Tunnel : by William 
Macdonough Agar, Ph.D., with a chapter by Robert A. Cairns, 
C.E. ; 38 pp., 2 maps, 3 figs., 8 pis., 23 cm., 1927. 

Bulletins i, 9, 12, 17, 21, 25, 27, 28, 32, 35 and 38 are merely 
administrative reports containing no scientific matter. The other 
bulletins may be classified as follows : 

Geology: Bulletins 4, 6, 7, 8, 13, 18, 23, 24, 29, 30, 33, 40. 
Botany: Bulletins 3, 5, 10, 11, 14, 15, 36, 37. 
Zoology: Bulletins 2, 16, 19, 20, 22, 26, 31, 34, 39. 

These bulletins are sold and otherwise distributed by the State 
Librarian. Postage, when bulletins are sent by mail, is as follows : 

No. 



No. 



I $0.05 


No 


16 


$0.10 


No 


2^ 


$0.05 


3 -10 




17 


•05 




29 


.10 


4 .10 




18 


.10 




30 


.10 


5 .05 




19 


.10 




31 


.20 


8 .05 




20 


.20 




32 


•05 


9 -05 




21 


•05 




33 


.10 


10 .10 




22 


•25 




34 


•25 


II .10 




23 


•05 




35 


•05 


12 .05 




24 


.20 




36 


.10 


13 .10 




25 


•05 




37 


.10 


14 .20 




26 


.10 




38 


.05 


15 -lo 




27 


•05 




39 


•15 


le prices when the bulletins are sold are as follows, postpaid: 


I $0.10 


No 


16 


$0.40 


No 


28 


$0.10 


3 45 




17 


.10 




29 


.60 


4 .35 




18 


•30 




30 


•55 


5 -20 




19 


.50 




31 


1.60 


8 .20 




20 


.60 




32 


.10 


9 .10 




21 


.10 




33 


.60 


10 .40 




22 


2.15 




34 


2.15 


II -35 




^Z 


.20 




35 


.10 


12 .10 




24 


.70 




36 


1. 00 


13 45 




25 


.10 




37 


.60 


14 .90 




26 


•85 




38 


.10 


15 40 




^7 


.10 




39 


2.00 



Limited numbers of these Bulletins have been assembled in 
volumes substantially bound in cloth, plainly lettered, and sell for 
the following prices, postpaid: 

Volume I, containing Bulletins 1-5 $i-75 

Volume II, containing Bulletins 6-12 2.75 

Volume III, containing Bulletins 13-15 2.75 

Volume IV, containing Bulletins 16-21 2.50 

Volume V, containing Bulletin 22 2.75 

Volume VI, containing Bulletins 23-32 4.15 , 



Volume VII, containing Bulletins 33-35 



3-75 



It is intended to follow a liberal policy in gratuitously distrib- 
uting these publications to public libraries, colleges, and scientific 
institutions, and to scientific men, teachers, and others who require 
particular bulletins for their work, especially to those who are 
citizens of Connecticut. 

Applications or inquiries should be addressed to 

George S. Godard, 

State Librarian, 
Hartford, Conn, 

In addition to the State Survey bulletins enumerated above, 
considerable work has been done by the State Survey in coopera- 
tion with the United States Geological Survey. The reports 
of such investigations have been published by the United States 
Geological Survey. 



State Geological and Natural History Survey of 
Connecticut 



COMMISSIONERS 

John H. Trumbull, Governor of Connecticut 
James Rowland Angell, President of Yale University 
James Lukens McConaughy, President of Wesleyan University 
Rem sen Brinckerhoff Ogilby, President of Trinity College 
Charles Lewis Beach, President of Connecticut Agricultural College 
Benjamin Tinkham Marshall, President of Connecticut College for 
Women 

SUPERINTENDENT 

W. E. Brixton 
Agricultural Experiment Station, New Haven 

DISTRIBUTION AND EXCHANGE AGENT 

George S. Godard, State Librarian 
Hartford 



CATALOGUE SLIPS 



Connecticut. State geological and natural history survey. 

Bulletin No. 40. The Geology of the Shepaug Aqueduct 
Tunnel, Litchfield County, Connecticut. By W. M. Agar, with a 
chapter by R. A. Cairns, Hartford, 1927. 

38 pp., 8 pis., 2 maps, 3 figs., 23 cm. 

Agar, William Macdonough. 

The Geology of the Shepaug Aqueduct Tunnel, Litchfield 
County, Connecticut. By W. M. Agar, with a chapter by R. A. 
Cairns, Hartford, 1927. 

38 pp., 8 pis., 2 maps, 3 figs., 23 cm. 

(Bulletin No. 40, Connecticut geological and natural history survey) 

Geology. 

Agar, W. M., The Geology of the Shepaug Aqueduct Tunnel, 
Litchfield County, Connecticut, with a chapter by R. A. Cairns. 
Hartford, 1927. 

38 pp., 8 pis., 2 maps, 3 figs., 23 cm. 

(Bulletin No. 40, Connecticut geological and natural history survey) 



7297 



35 




University of 
Connecticut 

Libraries 



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